Polymer composition

ABSTRACT

A method of preparing a (meth)acrylate functionalised polymer comprising the steps of mixing together a monofunctional vinylic monomer with from 0.3-100% w/w (based on monofunctional monomer) of a polyfunctional vinylic monomer and from 0.0001-50% w/w of a chain transfer agent, reacting said mixture to form a polymer and terminating the polymerisation reaction before 99% conversion. The resulting polymers are useful as components of surface coatings and inks, as moulding resins or in curable compounds, e.g. curable moulding resins or photoresists.

This application is the national phase of international applicationPCT/GB99/00618 filed Mar. 12, 1999 which designated the U.S.

The present invention relates to a polymer composition, in particular toa branched polymer which has polymerisable double bonds and to a methodof preparation therefor.

Branched polymers are polymer molecules of a finite size which arebranched, often having many branches. Branched polymers differ fromcrosslinked polymer networks which tend towards an infinite size havinginterconnected molecules and which are generally not soluble. Branchedpolymers are usually soluble in solvents which dissolve analogous linearpolymers but have the advantage that solutions of branched polymers areusually less viscous than solutions of the same concentration of thecorresponding linear polymer having a similar molecular weight.Therefore solutions of branched polymers are easier to handle especiallyat high solids content and may be made using less solvent than solutionsof linear polymers. For this reason, branched polymers are usefuladditives to solvent-based coatings and inks, for example and they alsohave many other applications. Additionally, branched polymers also havea lower melt viscosity than analogous linear polymers and are useful forimproving melt processability in injection moulding, compressionmoulding, extrusion moulding or powder coatings.

Branched polymers may be made by a two-step process in which a linearpolymer containing branching sites is subjected to a furtherpolymerisation or modification step to form branches from the branchingsites. The inherent complications of a two-step process may beunattractive and make the resulting branched polymer expensive to use.Alternatively a one-step process can be used in which a polyfunctionalmonomer is present to provide functionality in the polymer chain fromwhich polymer branches may grow. However, a limitation on the use ofconventional one-step processes is that the amount of polyfunctionalmonomer must be carefully controlled, usually to substantially less thanabout 0.5%w/w in order to avoid extensive cross-linking of the polymerand the formation of insoluble gels. It is very unusual to avoidcrosslinking using this system, especially in the absence of a solventas diluent and/or at high conversion of monomer to polymer.

Polymers having residual polymerisable double bonds are alsoconventionally made by two-step processes because using conventionalpolymerisation processes, polymerisable groups in the polymer wouldpolymerise to form cross-linked polymer molecules. Typicallypolymerisable double bonds may be added to a functional polymer backboneby post-polymerisation reaction of the functional groups with a compoundwhich carries such a double bond. These two-step process have thedisadvantages of increased complexity and therefore cost compared tosimple polymer preparation methods.

GB-A-2294467 describes a branched polymethylmethacrylate polymer whichhas a molecular weight of 80,000-400,000 in which the molecular weightbetween the branching points is between 30,000 and 1,000,000 whichincludes 0.05-0.2% of a polyfunctional monomer and <0.5 mole % of achain transfer agent. U.S. Pat. No. 5,767,211, published Jun. 16, 1998,describes the synthesis of multi-functional hyperbranched polymers byfree-radical polymerisation of di- or tri-vinyl monomers in the presenceof a chain transfer catalyst and a non-peroxide free radical initiator.The resulting polymers are oily, low Tg materials.

EP-A-103199 describes copolymers of t-butyl acrylate with 0.1-3%polyfunctional acrylate and 1-30% of functional comonomer made bysolution polymerisation in the presence of a chain transfer agent. Thefunctional comonomer provides an active cross-linking site used to forma coating composition crosslinked by condensation chemistry.

U.S. Pat. No. 4,880,889 describes a pre-crosslinked soluble polymercontaining 10-60% of OH-functionalised monomer, 5-25% of a monomer withat least 2 olefinically unsaturated double bonds and 15-82% of furthermonofunctional monomers. The polymer composition is made by a solutionpolymerisation process in organic solvent at a low polymerised solidscontent of about 50% in order to produce an ungelled copolymer,using >0.5% of a polymerisation regulator. The polymers are used incrosslinked coatings where the OH group is reacted withmelamine-formaldehyde crosslinkers. U.S. Pat. No. 4,988,760 and U.S.Pat. No. 5,115,064 define similar compositions which includefunctionalised monomers having different cross-linkable groups whichinclude carboxyl and isocyanate.

U.S. Pat. No. 5,227,432 describes a process for making acrylatecopolymers with free double bonds in which an acrylate copolymer made bypolymerising a monomer mixture containing 5-60% of functionalisedmonomer, 3-30% of a monomer with at least 2 olefinically unsaturateddouble bonds and other monofunctional monomers is reacted in asubsequent stage with a compound having a functional group which canreact with the functional group of the polymer and which also has atleast one ethylinically unsaturated polymerisable double bond. This is atwo stage process, in that the polymer with functional group is made ina first stage and then compound which includes the ethylenicallyunsaturated double bond is reacted with the functional group in e.g. anesterification reaction.

WO 98/27121 describes an acrylate-functionalised acrylate copolymer madeby a two-stage process of forming a copolymer having an esterifiablefunctional group and subsequently esterifying the functional group witha compound having a polymerisable acrylate or methacrylate group, theesterification reaction being carried out in the presence of acarbodiimide compound.

There is therefore a need for a method of forming acrylate ormethacrylate functionalised polymers in a relatively simple way.

According to the invention we therefore provide a method of preparing apolymer which includes at least one polymerisable double bondcomprising:

(i) mixing together a monofunctional monomer having one polymerisabledouble bond per molecule with from 0.3-100% w/w (of the weight of themonofunctional monomer) of a polyfunctional monomer having at least twopolymerisable double bonds per molecule and from 0.0001-50% w/w (of theweight of the monofunctional monomer) of a chain transfer agent andoptionally a free-radical polymerisation initiator,

(ii) reacting said mixture to form a polymer,

(iii) terminating the polymerisation reaction when <99% of thepolymerisable (double bonds present in the mixture have reacted to formpolymer.

In a second aspect of the invention, we provide a polymer which includesat least one polymerisable double bond consisting of residues of:

i) a monofunctional monomer having one polymerisable double bond permolecule,

ii) 0.3-100% w/w (of the weight of the monofunctional monomer) of apolyfunctional monomer having at least two polymerisable double bondsper molecule;

iii) from 0.0001-50% w/w (of the weight of the monofunctional monomer)of a chain transfer agent and optionally

iv) a free-radical polymerisation initiator.

Such a polymer therefore does not contain residues of apost-polymerisation functionalisation reaction which is necessitated,for example, by preparing an acrylate-functionalised polymer by thetwo-stage processes of the prior art. However, when a (meth)acrylatefunctionalised polymer is prepared by the method of the presentinvention using a monomer which has a functional pendant group, e.g. OH,carboxyl or amine, then the polymer may be subjected topost-polymerisation reactions of that functional group if required.

By (meth)acrylate, we mean either methacrylate, acrylate or both typesof group.

All amounts in weight % are calculated based on the total weight ofmonofunctional monomer. For example, if 100 g of monofunctional monomer(which may be a mixture of different monofunctional monomers) is used,5% wt of polyfunctional monomer is 5 g on this basis.

For simplicity, a monomer having one polymerisable double bond permolecule will be referred to hereinafter as a monofunctional monomer(MFM) and a monomer having at least two polymerisable double bonds permolecule will be referred to as a polyfunctional monomer (PFM). Bypolymer which includes at least one polymerisable double bond we mean apolymer having a double bond which can take part in furtherpolymerisation reactions after it has been made. The polymersiabledouble bond may be pendant or terminal but preferably the polymerincludes at least one polymerisable double bond in a pendant group. Thepolymer which includes at least one polymerisable double bond may bereferred to hereinafter as a polymerisable polymer.

The monofunctional monomer may comprise any monomer which can bepolymerised by a free-radical mechanism such as methacrylates andacrylates, styrene and derivatives thereof (styrenics), vinyl acetate,maleic anhydride, itaconic acid, N-alkyl (aryl) maleimides and N-vinylpyrrolidone, vinyl pyridine, acrylamide, methacrylamide,N,N-dialkylmethacrylamides and acrylonitrile. Mixtures of more than onemonofunctional monomer may be used to produce a random, alternatingblock or graft copolymer. Preferred monofunctional monomers compriseacrylates and methacrylates, i.e. preferably the double bond is avinylic double bond of an acrylate methacrylate compound.

Examples of suitable monofunctional (meth)acrylate monomers includelower alkyl, i.e. C₁ to C₂₀ alkyl, (meth)acrylates, e.g. methyl(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl(meth)acrylate, iso-butyl (meth)acrylate, t-butyl (meth)acrylate,2-ethyl hexyl (meth)acrylate, octyl (meth)acrylate or dodecyl(meth)acrylate. Additionally, cyclic alkyl monomeric species may be usedsuch as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate anddicyclopentenyl (meth)acrylate. Functional monomers such as methacrylicacid and acrylic acid, hydroxy alkyl methacrylates such as hydroxy ethyl(meth)acrylate, hydroxypropyl (meth)acrylate and hydroxybutyl(meth)acrylate, glycidyl (meth)acrylate, dialkyl aminoalkyl(meth)acrylates such as dimethyl aminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethyl aminopropyl (meth)acrylate anddiethyl aminopropyl (meth)acrylate. By (meth)acrylate, we mean thateither the methacrylate or the analogous acrylate may be used.

By polyfunctional monomer, we mean a monomer which has at least twopolymerisable double bonds per molecule. We also include in the termpolyfunctional monomer reactive oligomers or reactive polymers orpre-polymers having at least two double bonds polymerisable via afree-radical mechanism. Examples of suitable bifunctional monomersinclude: ethylene glycol di(meth)acrylate, hexanediol di(meth)acrylate,tripropylene glycol di(meth)acrylate, butanediol di(meth)acrylate,neopentyl glycol di(meth)acrylate, diethylene glycol di(meth)acrylate,triethylene glycol di(meth)acrylate, dipropylene glycoldi(meth)acrylate, allyl (meth)acrylate, divinyl benzene and substitutedanalogues thereof. Trifunctional examples include: tripropylene glycoltri(meth)acrylate, trimethylol propane tri(meth)acrylate,pentaerythritol tri(meth)acrylate. Tetrafunctional monomers such aspentaerythritol tetra(meth)acrylate and hexafunctional monomers, e.g.dipentaerythritol hexa(meth)acrylate may also be used. Optionally, thepolyfunctional monomer may comprise a mixture of more than onepolyfunctional compound.

The polymerisable polymer may be formed using a reactive oligomer orreactive polymer or pre-polymer having at least two polymerisable doublebonds per molecule as the or one of the polyfunctional monomers. Weinclude such functional polymers and oligomers in the term“polyfunctional monomer” because the polymerisable double bonds, whichare preferably (meth)acrylate groups enable the reactive oligomer orreactive polymer to polymerise into the growing polymer molecules in thesame way as a simple polyfunctional monomer. Typical reactive oligomersinclude, but are not limited to, epoxy-(meth)acrylates, polyether(meth)acrylates, polyester-(meth)acrylates and urethane-(meth)acrylates.Typical reactive polymers include addition or condensation polymers suchas a styrene or acrylic copolymers containing pendant polymerisable(meth)acrylate groups or unsaturated polyesters. The molecular weightrange of the oligomer or reactive polymer may vary from 500-500,000g/mole. When such reactive oligomers or polymers are used to provide atleast a part of the polyfunctional monomers the amount of polyfunctionalmaterial included in the reaction process is normally much greater thanwhen simple monomers are used, due to the higher molecular weight ofsuch materials.

The amount of polyfunctional monomer present may be up to 100 wt % ofthe total initial monofunctional monomer concentration. Preferably, theamount of polyfunctional monomer present is 0.3-25%. e.g. 0.5-10% basedon monofunctional monomer when the polyfunctional monomer is a simplemonomer, i.e. not a reactive oligomer or polymer. When reactive polymersor oligomers are used then the concentration may vary up to about 50%w/w or greater.

The chain transfer agent may be chosen from a range of thiol compoundsincluding monofunctional and polyfunctional thiois. Monofunctionalthiols include propyl mercaptan, butyl mercaptan, hexyl mercaptan, octylmercaptan, dodecyl mercaptan, thioglycollic acid, mercaptopropionicacid, alkyl thioglycollates such as 2-ethyl hexyl thioglycollate oroctyl thioglycollate, mercaptoethanol, mercaptoundecanoic acid,thiolactic acid, thiobutyric acid. Polyfunctional thiols includetrifunctional compounds such as trimethylol propanetris(3-mercaptopropionate), tetrafunctional compounds such aspentaerythritol tetra(3-mercaptopropionate), pentaerythritoltetrathioglycollate, pentaerythritol tetrathiolactate, pentaerythritoltetrathiobutyrate; hexafunctional compounds such as dipentaerythritolhexa(3-mercaptopropionate), dipentaerythritol hexathioglycollate;octafunctional thiols such as tripentaerythritolocta(3-mercaptopropionate), tripentaerythritol octathioglycollate. Theuse of polyfunctional thiols is a useful way to increase the degree ofbranching in the polymer. Optionally, the chain transfer agent maycomprise a mixture of more than one type of compound.

The amount of chain transfer agent present may be up to 50 wt % of thetotal initial monofunctional monomer concentration. In a firstembodiment, the amount of chain transfer agent present is 0.1-20% w/w,e.g. 0.5-10%w/w based on monofunctional monomer. The polymerisablepolymer is made using an appropriate amount of chain transfer agent toprevent the formation of a substantial amount of insoluble cross-linkedpolymer. The majority of the polymer produced is soluble, even at highconversion of monomer to polymer. A small amount of cross-linked polymermay be formed but the reaction conditions and level of chain transferagent should preferably be chosen such that the amount of cross-linkedpolymer formed is <10% (w/w), more preferably <5% (w/w), more preferably<2.5% (w/w) and optimally 0% (w/w). We have found that the use ofsecondary mercaptans as chain transfer agents leads to a reduction inthe level of cross-linked polymer and reduces the formation of microgelsin solutions of the resulting branched polymers. Therefore, for certainpolymerisation systems, the use of secondary mercaptan chain transferagents may be preferred. Chain transfer agents comprising secondarymercaptans are particularly preferred when the polymerisation is carriedout in bulk or suspension polymerisation processes.

Alternative chain transfer agents may be any species known to reducemolecular weight in the conventional free-radical polymerisation ofvinyl monomers. Examples include sulphides, disulphides,halogen-containing species. Also, catalytic chain transfer agents suchas cobalt complexes, e.g. cobalt (II) chelates such as cobalt porphyrincompounds are useful chain transfer agents for the invention. Suitablecobalt chelates are known in the art and are described in WO 98/04603. Aparticularly suitable compound is bis(borondifluorodimethylglyoximate)cobaltate (II) also known as COBF. Catalytic chain transfer agents maybe used in relatively low concentrations compared to conventional thiolchain transfer agents, e.g. <0. 5% preferably <0.1% by weight, sincethey are generally highly effective at low concentrations. We havesurprisingly found that catalytic chain transfer compounds based oncobalt complexes may be very effectively used at concentrations of lessthan 0.05% (500 ppm) w, e.g. 0.0001-0.01%w (1-100 ppmw) based on monomerin the polymerisation process of the present invention to give solublebranched polymers.

The polymerisation of the monomers may be initiated by any suitablemethod of generating free-radicals such as by thermally induceddecomposition of a thermal initiator such as an azo compound, peroxideor peroxyester. Therefore the polymerisation mixture also preferablycontains a polymerisation initiator which may be any of those known andconventionally used in free-radical polymerisation reactions, e.g. azoinitiators such as azobis(isobutyronitrile) (AIBN),azobis(2-methylbutyronitrile), azobis(2,4-dimethylvaleronitrile),azobis(4-cyanovaleric acid), peroxides such as dilauroyl peroxide,tert-butyl peroxyneodecanoate, dibenzoyl peroxide, cumyl peroxide,tert-butyl peroxy-2-ethyl hexanoate, tert-butyl peroxy diethyl acetateand tert-butyl peroxy benzoate.

The polymerisation of the monomer mixture may be performed using anyfree-radical polymerisation method, e.g. solution, suspension, emulsionand bulk polymerisation methods may all be used. For some applicationsof the polymerisable polymers of the invention, the material is requiredin solid form. For these applications, it may be advantageous to producethe polymer by a non-solution method, e.g. suspension or bulkpolymerisation. Surprisingly a soluble acrylate-functionalised branchedpolymer may be successfully formed from polyfunctional monomers in anon-solution method because the formation of gels would be expected. Forexample, U.S. Pat. No. 4,880,889 teaches that special reactionconditions, including carrying out the polymerisation in solution at arelatively low solids content of about 50%, are required to obtainungelled polymer.

Therefore in a further aspect of the invention, we provide a method ofpreparing a polymer which includes at least one polymerisable doublebond comprising:

(i) mixing together a monofunctional monomer having one polymerisabledouble bond per molecule with from 0.3-100% w/w (of the weight of themonofunctional monomer) of a polyfunctional monomer having at least twopolymerisable double bonds per molecule and from 0.0001-50% w/w (of theweight of the monofunctional monomer) of a chain transfer agent;

(ii) dispersing the resulting mixture as a discontinuous phase in acontinuous phase in which the monomers are relatively insoluble in thepresence of a dispersing agent which is capable of maintaining themixture of monomers as a discontinuous phase in the continuous phase;

(iii) initiating polymerisation of the monomer mixture;

iii) maintaining the dispersion of monomer in continuous phase at areaction temperature for sufficient time to enable the monomers to reactto form a polymer;

iv) terminating the polymerisation reaction when <99% of thepolymerisable (meth)acrylate groups present in the mixture have reactedto form polymer; and

v) subsequently separating the dispersed phase containing the polymerfrom the continuous phase.

The polymerisable polymer preferably contains pendant (meth)acrylategroups. The continuous phase is normally water. Suitable dispersingagents are well known in the art and include modified cellulose polymers(e.g. hydroxy ethyl, hydroxy propyl, hydroxy propyl methyl), polyacryticacid, polymethacrylic acid, partially and fully neutralised versions ofthese acids, poly(vinyl alcohol), poly(vinyl alcohol/vinyl acetate)copolymers amongst others. The dispersion of monomers in the continuousphase is normally agitated at high speed throughout the polymerisationprocess to help keep the dispersion stable and to enable good heattransfer between the continuous phase and the dispersed droplets orparticles. As the polymerisation reaction proceeds, the monomers in thedispersed phase react to form polymer which remains within the dispersedphase. The reaction temperature may vary according to the type ofmonomers and initiator which is used and is typically between 20 and150° C., for example in the range 50-120° C. Suitable reactiontemperatures are well known in the art.

Bulk polymerisation methods may be used, although they are lesspreferred. Typically in a bulk polymerisation, the monomer mixture isplaced in a sealed container, e.g. a bag, together with the initiatorand chain transfer agent and heated to a suitable polymerisationtemperature between 50 and 150° C. until the desired conversion has beenachieved. Normally the temperature is varied throughout the reactiontime to control the rate of polymerisation as the reaction proceeds.Such methods are known in the art to make acrylic polymers.

The polymerisation is terminated before completion, i.e. before 100%conversion and in this way polymerisable polymers, e.g. branchedpolymers which have acrylate functionality can be produced. Suchpolymers may then be further reacted, isolated and/or formulated into acurable composition and then reacted with other polymerisable orcross-linking species to form cured or cross-linked polymeric materials.Preferably the polymerisation reaction is terminated at a conversion of80-98%, more preferably 85-97%.

The polymerisation reaction may be terminated by cooling the reactionmixture or by adding a polymerisation inhibitor to the reaction mixturebefore the monomer has been completely converted to polymer. Suitableinhibitors include (optionally substituted) hydroquinones, e.g. methylhydroquinone or other species known to have an inhibiting effect onvinylic polymerisations such as t-butyl catechol, substituted phenolics,e.g. 2,6-t-butyl(4-nonylphenol), phenothiazine and substitutedanalogues.

Alternatively the polymerisation may be terminated before completeconversion of monomer by selecting a combination of initiator type,initiator concentration, polymerisation temperature and polymerisationtime such that the initiator is used up, i.e. the availability of freeradicals to initiate polymerisation becomes less and stops, before allof the available monomer has been polymerised. Therefore thepolymerisation reaction is initiated using a combination of initiatortype, initiator concentration, polymerisation temperature andpolymerisation time such that the availability of free radicals toinitiate polymerisation is insufficient to convert all polymerisablegroups in the monomer mixture to polymer.

In conventional polymensation reactions initiators are chosen to ensurethat sufficient free-radicals are available to react the monomer tocomplete conversion in an appropriate time. Sometimes a mixture ofinitiators is selected to provide desired polymerisation rates. Theactivity of thermal initiators is often measured and specified as the10-hour half-life temperature. Thermal initiators are chosen to have anappropriate half-life at the temperature of polymerisation. A preferredapproach in the method of this invention is to select an initiator or acombination of initiators which has a relatively short half-life at thepolymerisation temperature. The selection of short half-life or “fast”initiators is well known in the art.

The half life (t_(½)) of a thermal initiator is the time required toreduce the original initiator content at a given temperature to 50% andmay be determined by differential scanning calorimetry of dilutesolutions of the initiator in monochlorobenzene. Initiator half livesand 10-hour half-life temperatures are usually readily available frommanufacturers' literature, e.g. “Initiators for PolymerProduction—Product Catalog” from Akzo Nobel. AIBN has a 10-hourhalf-life temperature of 64° C.

AIBN is suitable for producing high conversion of (meth)acrylatemonomers to acrylic polymers at a polymerisation temperature of 75° C.At this polymerisation temperature, a faster initiator which has a10-hour half-life temperature of less than 64° C. is preferred for themethod of the invention. Suitable fast initiators include2,2′-azobis(2,4-dimethylvaleronitrile) which has a 10-hour half-lifetemperature of 52° C. and t-butylperoxyneodecanoate which has a 10-hourhalf-life temperature of 46° C.

Alternatively the amount of initiator may be selected to be insufficientto effect complete conversion of the monomers at the polymerisationtemperature.

The polymerisable e.g. (meth)acrylate-functionalised polymers of theinvention are useful as components of a number of surface coatingscompositions including paints, clear varnishes, inks and adhesives. Theymay be particularly useful as components in radiation-curableformulations in which the coating constituents, including thepolymerisable polymer, are dissolved or dispersed in a polymerisableliquid which polymerises in the presence of radiation (such as UV,light, electron-beam, infra-red or heat). Such coatings may alsocross-link or polymerise over a relatively longer period of time in theabsence of radiation. Curing or cross-linking of the polymerisablepolymers within a coating may impart superior solvent resistance,hardness and resistance to shrinkage. Coatings containing such polymersmay also show improved adhesion and faster drying or curing speeds. Thepolymerisable polymers made by the method of the invention are branchedin nature and this property may improve solubility in monomers orsolvents compared to comparable linear polymers. For application in suchcoating formulations, the polymerisable, e.g.(meth)acrylate-functionalised polymer may be supplied without removingresidual monomer (if any) from the polymerisation process because theresidual monomer may be the same as or compatible with a polymerisableliquid forming a constituent of the coating formulation. For example,when a (meth)acrylate-functionalised polymer is made using MMA as amonofunctional monomer, the resulting polymer, containing some unreactedMMA, is suitable for use in a coating formulation based on MMA withoutremoval of residual monomer.

The functional polymers are also useful in coatings applications such aspowder coatings and hot-melt adhesives (conventional andradiation-cured) which do not require the use of a diluent. In additionto surface coatings applications, the branched polymers of the inventionare useful for the preparation of bulk polymer articles via injectionmoulding, compression moulding or extrusion moulding. The polymerisablepolymers may also be used as constituents of compositions for use inother applications in which acrylic polymers are cured in situ, e.g. inpolymer-in-monomer syrups for reactive flooring, filled mouldingcompositions for moulding of e.g. kitchen sinks, worktops, acrylicsheets, shower trays, curable cements, photoresists, adhesives(including pressure-sensitive adhesives) etc. The polymerisable branchedcopolymers of the invention may be used alone or blended with otherpolymers in the end-use application.

In another aspect of the invention we provide a surface coatingcomposition comprising a branched polymerisable polymer which comprisesresidues of a polymer which includes at least one polymerisable(meth)acrylate group, said polymer consisting of residues of:

i) a monomer having one polymerisable (meth)acrylate group per molecule,

ii) 0.3-100% w/w (of the weight of the monomer having one polymerisable(meth)acrylate group per molecule) of a monomer having at least twopolymerisable (meth)acrylate groups per molecule;

iii) from 0.0001-50% w/w (of the weight of the monomer having onepolymerisable (meth)acrylate group per molecule) of a chain transferagent and optionally

iv) a free-radical polymerisation initiator.

The surface coating composition typically also may include polymerisablespecies such as monomers, functionalised oligomers and copolymers andother compounds such as cross-linking species, polymers, curing agents,colourants, solvents, dispersing aids, lubricants, processing aids,fillers, carrier fluids and toughening agents, plasticisers,flexibilisers, stabilisers, perfumes and other components asappropriate.

In a further aspect of the invention, we provide a polymeric article orcoating comprising

1) a branched polymerisable polymer consisting of residues of:

i) a monomer having one polymerisable (meth)acrylate group per molecule,

ii) 0.3-100% w/w (of the weight of the monomer having one polymerisable(meth)acrylate group per molecule) of a monomer having at least twopolymerisable (meth)acrylate groups per molecule;

iii) from 0.0001-50% w/w (of the weight of the monomer having onepolymerisable (meth)acrylate group per molecule) of a chain transferagent and optionally

iv) a free-radical polymerisation initiator and optionally

2) other compounds selected from monomers, functionalised oligomers andcopolymers and other compounds such as cross-linking species, polymers,curing agents, colourants, solvents, dispersing aids, lubricants,processing aids, fillers, carrier fluids and toughening agents,plasticisers, flexibilisers, stabilisers and perfumes.

The weight average molecular weight (Mw) of the acrylate-functionalisedbranched polymer is preferably in the range 2,000-500,000. For certainapplications, e.g. where dissolution of the branched polymer isrequired, a lower molecular weight, e.g. in the range 2,000-200,000 maybe preferred.

The invention will now be further described with reference to thefollowing Examples. In all examples, MFM refers to monofunctionalmonomer, PFM to polyfunctional monomer and CTA to chain transfer agent.The quantities of materials used in the polymerisations are calculatedas w/w with respect to the total concentration of monofunctionalmonomer. The weights of polyfunctional monomer, chain transfer agent andinitiator used, described as a weight % is calculated as a percentage ofthe weight of total monofunctional monomer. For example, for apolymerisation of MFM involving 3% PFM and 4% CTA, 3g of PFM and 4g ofCTA would be added to 100 g of MFM.

Preparation of Polymers by Suspension Polymerisation

Polymers were prepared by suspension polymerisation of a monomer mixturecontaining monofunctional and polyfunctional monomers in the presence ofthe chain transfer agent, e.g. dodecyl mercaptan (DDM), a dispersant(hydroxy ethyl cellulose, 1-2% by weight on monomer) and a free-radicalinitiator (AIBN, 1% by weight on monomer) in deionised water. In atypical preparation. 2000 ml deionised water and about 4 g hydroxy ethylcellulose (HEC) were added to a 5000 ml baffled flask. Nitrogen waspurged through the water for 30 minutes to remove dissolved oxygen andthe flask was agitated with a stainless steel stirrer set at 1400 rpm.The CTA was dissolved into the monomer mixture (500 g of the MFM mixedwith the required amount of PFM), and then added to the reaction flaskfollowed by the AIBN. The reaction flask was heated at full power to 75°C. and then the heating was reduced. The reaction was allowed to proceeduntil the exotherm began to subside. The maximum polymerisationtemperature was typically 90° C. The flask was left to heat treat for 1hr. The flask and contents were cooled with air to 40° C. and thecontents were dewatered by centrifuging. The polymers were dried ineither an oven at 40° C. or in a fluidised bed dryer.

This basic suspension polymerisation method was varied to terminate thepolymerisation before complete conversion to provide polymerisablepolymers as described in the examples below.

Preparation of Polymers by Solution Polymerisation

Polymers were made by solution polymerisation by dissolving MMA intoluene (33% w/w), adding the chosen concentration of polyfunctionalmonomer (MFM) and chain transfer agent (CTA) and initiatingpolymerisation using AIBN (1% by weight based on monomer).Polymerisations were performed at 80° C. in an oil bath under nitrogenusing a condenser. Polymerisations were terminated by cooling and byadding inhibitor as described below.

Characterisation by GPC

The molecular weight was measured by Gel Permeation Chromatography usingmixed gel columns and narrow molecular weight PMMA standards forcalibration. Chloroform was used as the mobile phase with a flow rate of1 ml/min and an infra-red detector. The weight average molecular weight(Mw), the number average molecular weight (Mn) and the polydispersity(Mw/Mn) were determined.

Determination of Solution Viscosities

The viscosity of a 30% (w/w) solution of the polymer in toluene wasmeasured using a Brookfield Viscometer at a temperature of 25° C. usingan LV2 spindle.

MMA is methyl methacrylate

BMA is n-butyl methacrylate

EMA is ethyl methacrylate

MAA is methacrylic acid

TPGDA is tripropylene glycol diacrylate

TMPTA is trimethylol propane triacrylate

PETA is pentaerythritol tetraacrylate

DPEHA is dipentaerythritol hexaacrylate

EGDMA is ethylene glycol dimethacrylate

TRIMP is trimethylol propane tris(3-mercaptopropionate)

PETMP is pentaerythritol tetramercaptopropionate

DPEHTG is dipentaerythritol hexathioglycollate

DDM is dodecyl mercaptan

EXAMPLES 1-5

Polymers were made by the suspension polymerisation of MMA and TPGDA inthe presence of DDM.

A polymerisation time of 43 minutes at 90° C. was established to obtain99% conversion of monomer. Polymers with pendant acrylate groups wereobtained by adding inhibitor at shorter polymerisation times. This wasachieved by adding a 2% aqueous solution of hydroquinone, equivalent to0.05% hydroquinone on monofunctional monomer. The samples wereimmediately cooled with air for 10 minutes to 40° C. The resultingpolymers were subsequently analysed by NMR spectroscopy and the % ofpendant acrylate groups was calculated. Molecular weights weredetermined by GPC. The acrylate % is the number of unreacted pendantacrylates as a fraction of the total of acrylate groups in the TPGDAincorporated.

TABLE 1 MeHQ TPGDA DDM time conversn acrylate Mn Mw Example wt % wt %(min) % % (g/mole) (g/mole) 1 3 4 none 99 — 6,900 43,000 (comparative) 23 4 40 97 21 6,450 34,500 3 3 4 38 96.3 24 5,800 32,000 4 3 4 33 92.3 445,050 18,850 5 3 4 30 94.1 59 5,100 15,950

EXAMPLES 6-21 Use of Acrylate-functionalised Polymers in Clear Varnishes

Acrylate-functionalised polymers were made by solution polymerisation,stopping the polymerisation by removing the polymerisation from thewater bath followed by the addition of 0.05%w based on polymer ofTopanol-A™ (Great Lakes Chemicals) inhibitor, resulting in approximately85-90% conversion of monomer to polymer. All polymerisations were basedon MMA as monofunctional monomer and the polyfunctional monomer shown inTables 2 & 3. A linear control polymer (Example 13) was made bypolymerising MMA in the absence of polyfunctional monomer. All polymerswere isolated by precipitation in hexane followed by drying in a vacuumoven at 50° C.

Clear varnish coating compositions were prepared using theacrylate-functionalised polymer, tripropylene glycol diacrylate asmonomer and Ebecryl™ 605 (UCB Chemicals) epoxy acrylate oligomer orEbecryl™ 4858 urethane-acrylate oligomer. Darocur™ 1173 (Ciba-Geigy) wasused as photoinitiator with an amine synergist Ebecryl™ P115. Thecoating formulations were:

wt % Acrylate-functionalised polymer 15 TPGDA 50 oligomer 25 Darocur1173 5 Ebecryl P115 5

The formulations were coated on to paper substrates to a thickness of 12μm. The coatings were then cured using a Primarc UV curing unit with ahigh-pressure mercury lamp light source at a power of 80 W.cm⁻². Theoptimum cure rate was assessed by establishing the maximum rate at whicha surface tack-free film was obtained. The cured coatings were thentested for solvent resistance and gloss. Solvent resistance wasdetermined in respect of methyl ethyl ketone (MEK). The cured coatingwas rubbed with a cloth saturated with MEK and the number of double rubsrecorded at the failure of the coating. The results are shown in Tables2 & 3 and demonstrate that the coatings containingacrylate-functionalised branched polymers have cure rates similar to orfaster than the coating containing linear non-functionalised polymer andsuperior solvent resistance.

TABLE 2 Coatings containing Ebecryl 605 epoxy acrylate oligomer solventPolyfunctional monomer Chain transfer agent cure resistance TPGDA TMPTAPETA DPEHA DDM TRIMP PETMP DPEHTG rate (double wt % wt % wt % wt % wt %wt % wt % wt % (m/min) rubs) 6 1.5 — — — 2 — — — 48 125 7 —  1.48- — — 2— — — 52 171 8 — — 1.76 — 2 — — — 52 195 9 — — — 2.89 2 — — — 52 250 10— 1.48 — — — 3.98 — — 48 155 11 — — 1.76 — — — 4.88 — 48 145 12 — — —2.89 — — — 6.98 48 117 13 — — — — 3.2 — — — 48  80

TABLE 3 Coatings containing Ebecryl 4858 urethane-acrylate oligomerPolyfunctional monomer Chain transfer agent cure TPGDA TMPTA PETA DPEHADDM TRIMP PETMP DPEHTG rate wt % wt % wt % wt % wt % wt % wt % wt %(m/min) 14 1.5 — — — 2 — — — 39 15 —  1.48- — — 2 — — — 39 16 — — 1.76 —2 — — — 39 17 — — — 2.89 2 — — — 43 18 — 1.48  — — — 3.98 — — 36 19 — —1.76 — — — 4.88 — 32 20 — — — 2.89 — — — 6.98 32 21 — — — — 3.2 — — — 20

EXAMPLES 22-25

Polymers were made by suspension polymerisation in a similar fashion toexamples 1-5. Molecular weights were determined by GPC. The polymerswere dissolved in TPGDA monomer at 30% w/w and the resulting solutionwas mixed 50/50 with a UV-curing ink based on black pigment, epoxyacrylate oligomer, TPGDA monomer and photoinitiator. Inks were coatedwith wire bars to produce coat thicknesses of approximately 20 μm. Curerate and solvent resistance were measured as described in Examples 6-21.Ink viscosity was measured by Brookfield viscometer at 25° C. Resultsand polymer compositions are shown in Table 4.

TABLE 4 solvent TPGDA DDM viscosity cure rate resistance Example MFM wt% wt % (cP) (m/min) (double rubs) 22 MAA/nBMA/EMA 0 0.4 5,260 <20  120(3:39:58) 23 MMA 3 4 2,860 28 >400 24 MMA 3 4 2,250 20 >400 25MMA/BMA/MAA 3 4 2,650 20 >400 (95.5:3:1.5) 26 MMA/BMA/MAA 3.5 4 3,29020 >400 (67.5:31:1.5)

EXAMPLE 26 Fast Initiator

Polymers were made by the suspension polymerisation of MMA and 3% wtTPGDA in the presence of 4% wt DDM as described in the general methodbut using an equimolar quantity of Vazo 52 in place of AIBN. Noinhibitor was added to the polymerisation. Vazo 52 is a commerciallyavailable free-radical initiator based on 2,2640-azobis(2,4dimethylvaleronitrile). The resulting polymer had Mn=6,600g/mole, Mw=30,050 g/mole, the residual monomer was 4%, and the polymercontained unreacted acrylate groups. cl EXAMPLE 27

Bulk Polymerisation

MMA, 3% TPGDA, 4% DDM and 0.5% lauroyl peroxide are weighed out andtransferred to a nylon bag, which is sealed ensuring no air bubbles arepresent. This is then placed in an oven with a programmed temperaturecycle running from 55° C. to 120° C. over 40 hours in a step-wisepattern. The resulting polymer had residual MMA of 13%w/w, Mn=7,050 andMw=42,700 and contained residual acrylate functionality.

What is claimed is:
 1. A method of preparing a polymer which includes atleast one polymerisable double bond which comprises: (i) mixing togethera monofunctional monomer having one polymerisable double bond permolecule with 0.3-100% w/w (of the weight of the monofunctional monomer)of a polyfunctional monomer having ea least two polymerisable doublebonds per molecule and from 0.0001-50% w/w (of the weight of themonofunctional monomer) of a chain transfer agent and optionally afree-radical polymerisation initiator, said monofunctional monomercomprising at least one of methyl (meth)acrylate, n-butyl(meth)acrylate, iso-butyl (meth)acrylate, t-butyl (meth)acrylate ormethacrylic acid and said polyfunctional monomer comprising at least oneof bi-functional (meth)acrylates, tri-functional (meth)acrylates,tetra-functional (meth)acrylates, penta-functional (meth)acrylates,hexa-functional (meth)acrylates, oligomers or polymers having at leasttwo polymerisable (meth)acrylate groups per molecule, and mixturesthereof (ii) reacting said mixture to form a polymer, and (iii)terminating the polymerisation reaction when 80 to 98% of thepolymerisable double bonds present in the mixture have reacted to formpolymer.
 2. A method as claimed in claim 1, wherein the monofunctionalmonomer comprises a mixture of more than one monofunctional monomer. 3.A method as claimed in claim 1, wherein the polyfunctional monomercomprises at least one of ethylene glycol di(meth)acrylate, hexanedioldi(meth)acrylate, tripropylene glycol di(meth)acrylate, butanedioldi(meth)acrylate, neopentyl glycol di(meth)acrylate, diethylene glycoldi(meth)acrylate, triethylene glycol di(meth)acrylate, dipropyleneglycol di(meth)acrylate, allyl (meth)acrylate and substituted analogsthereof.
 4. A method as claimed in claim 1, wherein the chain transferagent is selected from monofunctional and polyfunctional thiols.
 5. Amethod as claimed in claim 1, wherein the reaction is terminated by theaddition of a polymerisation inhibitor to the reaction mixture and/or bycooling the reaction mixture.
 6. A method as claimed in claim 1, whereinthe polymerisation reaction is initiated using a combination ofinitiator type, initiator concentration, polymerisation temperature andpolymerisation time such that the availability of free radicals toinitiate polymerisation is insufficient to convert all polymerisablegroups in the monomer mixture to polymer.
 7. A method as claimed inclaim 6, wherein the polymerisation is carried out at a temperature inthe range 70-80° C. using an initiator which has a 10-hour half-lifetemperature of less than 64° C.
 8. A method as claimed in claim 7,wherein the initiator is selected from2,2′-azobis(2,4-dimethylvaleronitrile) and t-butylperoxyneodecanoate. 9.A method as claimed in claim 1, wherein the polymerisation reaction isterminated when 85%-97% of the polymerisable double bonds present in themixture have reacted to form polymer.
 10. A method of preparing apolymer which includes at least one polymerisable double bond whichcomprises: (i) mixing together a monofunctional monomer having onepolymerisable double bond per molecule with 0.3-100% w/w (of the weightof the monofunctional monomer) of a polyfunctional monomer having atleast two polymerisable double bonds per molecule and from 0.0001-50%w/w (of the weight of the monofunctional monomer) of a chain transferagent and optionally a free-radical polymerisation initiator, saidmonofunctional monomer comprising at least one of methyl (meth)acrylate,n-butyl (meth)acrylate, iso-butyl (meth)acrylate, t-butyl (meth)acrylateor methacrylic acid and said polyfunctional monomer comprising at leastone of bi-functional (meth)acrylates, tri-functional (meth)acrylates,tetra-functional (meth)acrylates, penta-functional (meth)acrylates,hexa-functional (meth)acrylates, oligomers or polymers having at leasttwo polymerisable (meth)acrylate groups per molecule, and mixturesthereof (ii) reacting said mixture to form a polymer, and (iii) addingpolymerisation inhibitor to the reaction mixture to terminate thepolymerisation reaction when 80 to 98% of the polymerisable double bondspresent in the mixture have reacted to form polymer.
 11. A method asclaimed in claim 10, wherein the polymerisation inhibitor is added tothe reaction mixture to terminate the polymerisation reaction when85%-97% of the polymerisable double bonds present in the mixture havereacted to form polymer.
 12. A method of preparing a polymer whichincludes at least one polymerisable double bond which comprises: (i)mixing together a monofunctional monomer having one polymerisable doublebond per molecule with 0.3-100% w/w (of the weight of the monofunctionalmonomer) of a polyfunctional monomer having at least two polymerisabledouble bonds per molecule and from 0.0001-50% w/w (of the weight of themonofunctional monomer) of a chain transfer agent and optionally afree-radical polymerisation initiator, said monofunctional monomercomprising at least one of methyl (meth)acrylate, n-butyl(meth)acrylate, iso-butyl (meth)acrylate, t-butyl (meth)acrylate ormethacrylic acid and said polyfunctional monomer comprising at least oneof bi-functional (meth)acrylates, tri-functional (meth)acrylates,tetra-functional (meth)acrylates, penta-functional (meth)acrylates,hexa-functional (meth)acrylates, oligomers or polymers having at leasttwo polymerisable (meth)acrylate groups per molecule, and mixturesthereof (ii) reacting said mixture to form a polymer, and (iii) coolingthe reaction mixture to terminate the polymerisation reaction when 80 to98% of the polymerisable double bonds present in the mixture havereacted to form polymer.
 13. A method as claimed in claim 12, whereinthe reaction mixture is cooled to terminate the polymerisation reactionwhen 85%-97% of the polymerisable double bonds present in the mixturehave reacted to form polymer.
 14. A method as claimed in claim 3,further comprising isolating the resulting polymer having acrylatefunctionality and formulating the isolated polymer into a curablecomposition.
 15. A method of preparing a polymer which includes at leastone polymerisable double bond which comprises: (i) mixing together amonofunctional monomer having one polymerisable double bond per moleculewith 0.3-100% w/w (of the weight of the monofunctional monomer) of apolyfunctional monomer having at least two polymerisable double bondsper molecule and from 0.0001-50% w/w (of the weight of themonofunctional monomer) of a chain transfer agent and a free-radicalpolymerisation initiator, said monofunctional monomer comprising atleast one of methyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl(meth)acrylate, t-butyl (meth)acrylate or methacrylic acid and saidpolyfunctional monomer comprising at least one of bi-functional(meth)acrylates, tri-functional (meth)acrylates, tetra-functional(meth)acrylates, penta-functional (meth)acrylates, hexa-functional(meth)acrylates, oligomers or polymers having at least two polymerisable(meth)acrylate groups per molecule, and mixtures thereof and (ii)reacting said mixture to form a polymer, and wherein the type andconcentration of the polymerisation initiator, polymerisationtemperature and polymerisation time are selected such that theavailability of free radicals to initiate polymerisation is insufficientto convert all polymerisable groups in the monomer mixture to polymer,whereby the polymerisation reaction is terminated when 80 to 98% of thepolymerisable double bonds present in the mixture have reacted to formpolymer.
 16. A method as claimed in claim 15, wherein the type andconcentration of the polymerisation initiator, polymerisationtemperature and polymerisation time are selected such that theavailability of free radicals to initiate polymerisation is insufficientto convert all polymerisable groups in the monomer mixture to polymer,whereby the polymerisation reaction is terminated when 85 to 97% of thepolymerisable double bonds present in the mixture have reacted to formpolymer.
 17. A method as claimed in claim 1, wherein the polyfunctionalmonomer comprises at least one of tripropylene glycol tri(meth)acrylate,trimethylol propane tri(meth)acrylate and pentaerythritoltri(meth)acrylate.
 18. A method as set forth in claim 1, wherein thepolyfunctional monomer comprises at least pentaerythritoltetra(meth)acrylate.
 19. A method as set forth in claim 1, wherein thepolyfunctional monomer comprises at least dipentaerythritolhexa(meth)acrylate.